Application of Ultrasonography to the Investigation of Follicular Dynamic in Synchronized 'Goudali' Zebu Females. A transrectal ultrasonography was used to follow the follicular dynamics in 8 'Goudali' zebu females. Three treatments were used to synchronize estrus: Group 1: Crestar implant associated to PGF2 and PMSG (n= 4); Group 2: Crestar implant associated to PMSG (n= 2) and Group 3: Crestar implant associated to PGF2 (n= 2). The ultrasonographic examinations were performed as follows: day of implant introduction, day of implant removal, and at 4 hour interval between the 28th and the 56th hour after implant removal. The ovaries were examined 7 days after ovulation to determine the number of corpora lutea. The numbers of 2-3 mm diameter follicles observed at the day of implant removal were 5.8 ± 2.2; 3.5 ± 0.7 et 4.5 ± 0.7, respectively for Groups 1, 2 and 3. At the beginning of estrus (30.4 ± 4.9 hours after implant removal), a mean of 4.1 ± 1.3 follicles with 5-6 mm of diameter has been observed for the 3 groups. At the 36th hour after the end of the synchronization treatment, a mean of 1.1 ± 0.4 dominant follicles (> 8 mm) was observed. The diameter of pre-ovulatory follicles did not vary among groups. The first ovulations have been observed between 22 to 26 hours after the beginning of estrus.